240 THE LARCH. 



glandular lining, the matter of alburnum is deposited ; 

 and that which is not thus expended sinks into the 

 alburnum or sap wood, and there in part joins the 

 alburnus current. I say in part, because a part is 

 expended in giving additional solidity to the sapwood 

 of former years, and in converting part of that into 

 heart- wood, and in giving increased solidity to the heart- 

 wood previously formed. So long as the heart-wood 

 continues to receive new matter, I conceive it to live, and 

 no longer' In a former communication, Mr. Knight 

 had distinctly stated what the vessels were which, in 

 his opinion, conducted this elaborated sap into and 

 through the alburnum and inner concentric layers. 

 He observed, ' that the unemployed portion of sap 

 sinks into the alburnum through the misnamed medul- 

 lary processes.' These processes, which have also been 

 termed the divergent rays, appear to originate in the 

 liber, and to converge towards the medulla or pith, 

 but do not enter into it, nor certainly proceed from it. 

 I had long ago conjectured and said that I considered 

 the office of these rays or processes to be that of con- 

 veying laterally the prepared juices which were intended 

 to support the previously formed layers of wood ; and 

 in my letter to the Duke of Portland I stated that 

 the disease of the larch might arise from some cause 

 which prevented the elaborated resinous juices of the 

 leaves and bark from passing in sufficient quantity, by 

 the medullary or convergent processes, from the albur- 

 num laterally into the inner layers of the wood. Now, 

 if this view of the internal cause of disease be correct, 



